1. Field of the Invention
The present invention relates to a process for making an indium-tin-oxide (ITO) shaped body, to such a shaped body and to the use of such a shaped body.
2. Background Information
WO 97/31739 discloses among other features a process for making a pair of sputtering targets, wherein, in view of the sputtering loss, this is preformed to shape close to final shape by compaction of a metal powder between two massive plates under hot isostatic pressing conditions. The separating plates disposed on each side of an appropriate apparatus are adjacent to each other in pairs and are separated from each other by a ceramic release layer. The ceramic release layer prevents diffusion welding of the corresponding plates to each other. In this process, the powder is compacted substantially uniaxially despite hot isostatic pressing. The inhomogeneous compaction of the indium-tin-oxide (ITO) compact is therefore unfavorable.
Japanese Patent Application 5170513 discloses a process for making highly compact ITOs (indium-tin-oxide compounds), which are sintered using oxygen as the sintering atmosphere in a nickel or copper hollow vessel, the inside surface of which is coated with alumina and/or boron nitride. A disadvantage in this process is the wrinkling which occurs in the wall of the hollow vessel due to severe shrinkage of the powder filling during hot isostatic pressing.
Different coefficients of thermal expansion of the ITO and the material of the hollow-vessel wall lead to cracking and the risk of contamination of the ITO. Strong adhesion to the corresponding metal wall is also observed; both lead to cracking, and so it is not possible reliably to make predetermined dimensions and geometries for ITOs.
German Patent DE 29 39 634 C2 (U.S. Pat. No. 4,250,610 is a related family member of DE 2939634C2) relates to a process for compacting a metal casting at a high temperature under isostatic pressure ("hot isostatic pressing" or "HIP"), wherein the casting contains irregularities associated with the surface and a coating is applied on a surface of the casting in order to bridge over surface openings associated with the irregularities, after which the casting is subjected to a combination of selected processing temperature and isostatic pressure to bring about compaction. The coating comprises a ceramic material, which at a vitrification temperature lower than the selected processing temperature for compaction by the HIP yields a nonmetallic, amorphous ceramic coating which is substantially impermeable to gas. The coating therefore fuses during hot isostatic pressing.
The coefficient of thermal expansion is adapted to the coefficient of thermal expansion of the casting surface in the temperature range from room temperature up to the selected processing temperature for compaction.
At the selected processing temperature during compaction, the coating is viscous, and so the bond of the coating to the casting surface is destroyed during compaction by the HIP.
The casting surface and the ceramic material are heated to the vitrification temperature and the ceramic material vitrifies to form the ceramic coating, thus yielding a destroyable bond to the casting surface.
The coated casting is then cooled and the coated casting surface is subjected to a combination of a selected processing temperature and isostatic pressure, in order to compact the coated part of the casting and to destroy the bond between the ceramic coating and the casting surface.
Finally the casting is cooled and then the coating is removed from the surface thereof.
This hot isostatic pressing process developed especially for metal castings represents an extremely complicated and thus time-consuming and costly process, with the additional disadvantage that the viscous coating would penetrate into cold compacts made by powder metallurgy.